This invention relates to the alkylation of aromatic compounds and is particularly concerned with (1) a process for increasing the selectivity of an alkylation catalyst for monoalkylation, (2) alkylation catalysts that have been treated in such a manner as to improve their selectivity for monoalkylation and (3) alkylation processes using such catalysts of improved selectivity for monoalkylation.
In the past it has been common practice to alkylate aromatic molecules such as benzene, toluene and xylene with ethylene, propylene and other olefins using acidic Friedel-Crafts type catalysts or heterogeneous acidic silica-alumina catalysts. Such processes have several disadvantages including corrosion problems caused by Friedel-Crafts type catalysts and difficulty in controlling the product distribution obtained from the alkylation reactions. Normally, the desired product is the monoalkylate rather than the di or trialkylate. In an effort to avoid a large production of di and trialkylate products, it is conventional practice to use a large excess of the aromatic compound.
To avoid some of the problems associated with earlier commercial alkylation processes, solid zeolite-containing catalysts have been used in recent years to promote the alkylation of aromatic compounds with olefins and other alkylating agents, especially the alkylation of benzene with ethylene. Normally, these catalysts are used in a fixed bed reactor through which the reactants are continuously passed. Although such fixed bed processes using zeolite-containing catalysts have advantages over earlier commercial processes, the selectivity and activity maintenance for monoalkylation, especially when producing cumene by reacting propylene with benzene, is not as high as desired and is often unsatisfactory.
Accordingly, it is one of the objects of the present invention to provide a process for increasing the selectivity and maintaining the activity of alkylation catalysts containing zeolites and other molecular sieves. It is another object of the invention to provide a molecular sieve-containing alkylation catalyst having an increased selectivity for monoalkylation and a process for alkylating an aromatic compound to form an alkylated aromatic using a catalyst having an increased selectivity for monoalkylation. These and other objects of the invention will become more apparent in view of the following description of the invention.